Terahertz elements and devices designed to work in the frequency range of 0.1-10 THz have attracted enormous research activities in the past decade or so due to its potential use in applications such as astronomical remote sensing, tag-free bio-molecular detection, and monitoring of harmful chemicals. Intensive studies on the generation, transmission and detection mechanisms of THz signals also demonstrated the possibility of building integrated circuits in THz frequency range, which is known to have broader bandwidth than the operating frequency range of the current-generation VLSI devices and circuits. A major hurdle encountered by designers of THz logic components is how to realize low-loss and low dispersion transmission of electromagnetic signals. One way to overcome the problem is to introduce periodic surface features such as holes, grooves, and dimples onto the material interface of the structure, which generates a special surface mode known as the Spoofed Surface Plasmon Polariton (SSPP). Such pseudo mode mimics the common optical surface plasmon mode traveling at dielectric-metal interface, and therefore has a similar mode profile with strongly confined E-M field and localized energy distribution.
By introducing one-dimensional (1-D) periodic grooves on opposite interfaces of metal-dielectric-metal waveguides, a doubly-corrugated SSPP (DC-SSPP) structure can be realized. Previous work has provided extensive theoretical study along with computer simulations to demonstrate the existence of discrete transmission bands as well as SSPP modes with close-to-zero group velocity in such DC-SSPP structures. It has also been shown that the spectral response of DC-SSPP structures strongly depends on the geometrical dimensions and the choice of building materials. As a result, a number of passive and active SSPP components such as frequency filters and Boolean switches have been proposed and the related research work has been reported in other publications.
A common issue in the design of THz components is to achieve better spectral selectivity in the form of sharper transmission peaks. Higher sensitivity to the structural change caused by external stimuli is also preferred in the design of sensors and active components alike. In this disclosure, an interferometer design is proposed which combines two arms of the DC-SSPP structure together to form a Mach-Zehnder interferometer (MZI). While the MZI structure is often used in other scenarios to realize signal controls based on phase delay, with the help of DC-SSPP structure this structure is applied to the terahertz frequency domain.
This section provides background information related to the present disclosure which is not necessarily prior art.